In electronics there is frequently a requirement for diminishing electrical or magnetic fields within or outside a specific area. Screening housings which attenuate the emission or entry of electromagnetic interference. On printed circuit boards the interference radiation can also be caused by subassemblies located on the same printed circuit board. With miniaturized subassembles, for example those using SMD technology, interference sinks and interference sources are often immediately adjacent to one another. For screening field values which change over time small designs of multipart screening devices are employed.
They mostly consist of a screening frame subdivided into individual chambers by partition walls and soldered to the printed circuit board. To keep the subassembles covered by the screening accessible for test purposes the screening frame is closed off by a removable cover. Since the frame part only becomes mechanically stable once it is soldered to the printed circuit board it is necessary, when fitting these miniaturized screening devices, to handle the frame part and the cover part together. Putting the cover on and taking it off is a cumbersome process and assembly is time-consuming.
A single-part metallic screening device which can be fitted onto a printed circuit board is known from DE 29 808 620 U1. It is attached by locking lugs which grip the back of the printed circuit board. Mass contacting of the screen with the printed circuit board is provided by a plurality of spring-loaded tongues. These tongues are under elastic pretension once a screening tray is assembled and make electrical contact by line or point contact. Under harsh operating conditions it can occur that contacting fails as a result of mechanical effects or corrosion. In this case the screening efficiency of the interference suppression medium is adversely affected. A further disadvantage is that a compression force is necessary on assembly of the screening cover to overcome the spring pressure, said force having to be applied to the screen tray and borne by the printed circuit board. The screening effect depends on the contacting spring pressure and the distance between the individual contact points. If however a large number of spring tongues have to be elastically deformed a correspondingly greater compression force is required and it can occur with miniaturized modules that the circuit board is impermissibly deformed. Micro cracks can then develop in the conductive structure.
Contact is also established by contact springs around the edge of the screening in the screening device known from DE 297 13 412 U1.
Manufacturing these known one-piece screening devices requires a complex manufacturing tool. Changes to this tool required to produce a new screening geometry or spatial form are only possible with a comparatively large amount of effort.